Air inductive ballast

ABSTRACT

In a ballast a synthetic resin block which swells in vacuo is urged against the connecting conductors of the coil in the ballast. Subsequently the air in the space around the coil is conducted away so that the synthetic resin envelops the connecting conductors. Subsequently an insulating moulding mass is provided around the coil and around the connecting conductors which are surrounded by the synthetic resin.

Unite States Patent Van Der Hoek Jan. 14, 1975 AIR INDUCTIVE BALLAST Inventor: Jan Lambertus Van Der Hoek,

Emmasingel, Eindhoven, Netherlands Assignee: U.S. Philips Corporation, New

York, NY.

Filed: Dec. 4, 1973 Appl. No.: 421,513

Related U.S. Application Data Division of Ser. No. 213,448, Dec. 29, 1971.

Foreign Application Priority Data Jan. 13, 1971 Netherlands 7100411 U.S. Cl 336/96, 174/52 PE, 264/272 Int. Cl. HOlf 27/02 Field of Search 336/96, 100; 174/52 PE;

[56] References Cited UNITED STATES PATENTS 2,392,311 H1946 Christopher 174/52 PE 3,163,838 12/1964 Antalis et al.... 336/96 X 3,670,091 6/1972 Frantz et al 174/52 PF,

Primary Examiner-Thomas J. Kozma Attorney, Agent, or FirmFrank R. Trifari [57] ABSTRACT In a ballast a synthetic resin block which swells in vacuo is urged against the connecting conductors of the coil in the ballast. Subsequently the air in the space around the coil is conducted away so that the synthetic resin envelops the connecting conductors. Subsequently an insulating moulding mass is provided around the coil and around the connecting conductors which are surrounded by the synthetic resin.

2 Claims, 10 Drawing Figures AIR INDUCTIVE BALLAST This is a division of application Ser. No. 213,448, filed Dec. 29, 1971.

The invention relates to a method of manufacturing an inductive ballast which is provided with a coil and a housing enveloping said coil, and electrical conductors for connection of the coil, in which at least a part of the combination of the coil and the part of the connection conductors located within the housing is covered with a synthetic resin which is provided with closed cells. The space between the said combination of coil and connection conductors and the wall of the housing is filled for the greater part with an insulating moulding mass.

When manufacturing an inductive ballast for stabilizing a discharge in a discharge lamp an insulating moulding mass has been known to be used. A polyester mixed with sand which is moulded around the coil of this arrangement is known. In this process the coil is placed in a housing and then the interior is evacuated through several small apertures in said housing and subsequently the polyester mass can flow into the housing through a second aperture and then hardens. An advantage of this known ballast is that the coil is satisfactorily insulated and that the heat from the coil is satisfactorily conducted away to the outer wall of the enveloping housing.

A drawback of these known ballasts is, however, that the moulding mass, for example, the polyester mass may crack due to shrinkage in the course of time. If these shrinkage cracks occur at areas where electrical conductors are present which extend from the coil to the exterior of the housing, a. pressure'may be exerted on these supply conductors such that they become defective. As a result the inductive ballast may be cut out of the circuit and cannot further operate.

It is also known to manufacture devices with a synthetic resin provided with closed cells such as described above. This synthetic resin is provided between the insulating moulding mass and parts of the electric unit. See, for example, Swiss Patent Specification 3 l6936. A drawback of the device described in this Swiss Patent Specification is, however, that a fairly large part of the coil is surrounded by the snythetic resin with its closed cells. This effects the conducting away of heat from this coil.

It is an object of the present invention to provide a ballast of the kind described in the introduction in which on the one hand the influence of possible shrinkage cracks in the hardened insulating moulding mass, which might lead tobreakage of the electrical conductors in the ballast, is prevented and in which furhermore the synthetic resin having closed cells used for this purpose is provided in a very simple manner around the electrical connecting conductors and in which finally the conducting away of heat from the coil of the finished ballast is satisfactory.

According to the invention an inductive ballast is provided with a coil and a housing enveloping said coil and electrical conductors for the connection of the coil, in which at least a part of the combination of the coil and the part of the connecting conductors located within the housing is covered with a synthetic resin which is provided with closed cells, and in which subsequently the space between the said combination of coil and connecting conductors on the one hand and the wall of the housing on the other hand is filled for the greater part with an insulating moulding mass is characterized in that a block of mainly elastically deformable synthetic resin is laid on the connecting conductors, the housing being subsequently substantially closed in such a manner that the space between these conductors and the adjacent wall of the housing is at least for a great part filled with the snythetic resin. The interior of the housing being subsequently substantially evacuated so that the synthetic resin swells and envelops the connecting conductors. The moulding mass is admitted in a liquid state to the interior of the housing and hardens in the housing.

An advantage of the invention is that the synthetic resin can be provided in a very simple manner around the connecting conductors. in this case use is made of the known evacuation of the housing so as to enable the moulding mass to flow in. When the synthetic resin swells upon evacuation it will envelope the connecting conductors. This advantage would not be adequately achieved with a sleeve of an insulating material provided around the connecting conductors. In fact, then the moulding mass could also creep between the connecting conductors and the sleeve upon evacuation of the interior of the housing.

The invention may be used, for example, in an inductive ballast for stabilizing the discharge in a discharge lamp, for example, a low-pressure mercury vapour discharge lamp. The use of the invention in other ballasts such as, for example, transformers is also possible.

It is feasible that each part of the block of synthetic resin is built up in the same manner. In that case the block of synthetic resin will tend to swell in all directions to an equal extent during evacuation of the housing because originally air of atmospheric pressure prevailed in the closed cells.

In a further embodiment according to the invention the side of the block of synthetic resin remote from the connecting conductors is not expandable and the support for the conductors is provided on the side of them which is remote from the synthetic resin block prior to providing the housing.

An advantage of this embodiment is that the side of the block of synthetic resin facing the conductors swells to a greater extent than the part which is remote from the conductors. As a result the block tends to assume a curved shape with its convex side facing the connecting conductors. Of advantage is that the connecting conductors are more firmly urged against the support which is on the other side of these conductors. Thus the conductors are adequately enveloped by the deformable synthetic resin, and the conductors are satisfactorily abutted against the support.

In a further embodiment the side of the block of synthetic resin remote from the connecting conductors does not have any stretching properties and the side of the synthetic resin block facing the connecting conductors is provided with a plurality of grooves parallel to the connecting conductors, the number of grooves being equal to the number of connecting conductors. The grooves are opened by curvature of the synthetic resin block during evacuation in such a manner that they can accommodate the connecting wires and closing again after flowing of the moulding mass, thus enveloping the connecting conductors.

An advantage of this embodiment is that the connecting conductors are surrounded by the synthetic resin even more effectively. A further advantage is that a support on the other side of the connecting conductors is not necessary in this case.

In order that the invention may be readily carried into effect, some embodiments thereof will now be described in detail by way of example with reference to the accompanying diagrammatic drawing in which:

FIG. 1 is a perspective view of a cover for a housing of a ballast according to the invention;

FIG. 2 is a perspective view of a ballast according to the invention during a given manufacturing stage;

FIG. 3 shows the ballast of FIG. 2 including a housing intersected along the longitudinal axis and a device for filling said ballast with a moulding mass;

FIG. 4 shows a detail of the ballast of FIG. 3 on a larger scale;

FIG. 5 shows the same detail as in FIG. 4 during a following manufacturing stage;

FIG. 6 is a cross-section taken on the line VIVi of the ballast of FIG. 3;

FIG. 7 shows the same cross-section as in FIG. 6 during a following manufacturing stage;

FIG. 8 shows another embodiment of the synthetic resin block for a ballast according to the invention as well as part of the cover for the housing of said ballast;

FIG. 9 shows the same part of FIG. 8 during a following manufacturing stage;

H0. 10 likewise shows the same ballast of FIGS. 8 and 9 during a still further manufacturing stage.

In FIG. 1 the reference numeral 1 denotes a cover for an inductive ballast for stabilizing a low-pressure mercury vapor discharge lamp. FIG. 2 is a perspective view of the other parts of this housing and its contents namely a coil for this housing. The cover 1 which is shown in FIG. 1 consists of steel having a thickness of approximately 0.8 mm. The reference numerals 2, 3, 4 and 5 denote holes for connecting said cover during a further manufacturing stage with the other parts of the housing which are shown in FIG. 2. The reference numerals 6 and 7 denote assembly holes for securing the complete housing to a longitudinal bar, for example, a lighting fixture.

In FIG. 2 the reference numeral 10 shows the trayshaped part of the housing. The reference numerals 11, 12 and 13 show connecting holes which correspond to the holes 2, 3 and 4 of FIG. 1. A fourth hole in the trayshaped housing 10 is not visible in FIG. 2 because a part of this tray 10 in this FIGURE is cut away. The tray-shaped housing 10 includes a coil which consists of a number of laminations l4 and an electrical winding 15. The laminations 14 are E-shaped and are formed in two packs.

The electrical winding 15 is provided with twoelectrical connecting conductors 16 and 17. These connecting conductors are passed to the exterior through the wall of the housing 10 and terminate in connection pins. Only one of these pins (reference numeral 18a) is shown in FIG. 2. Reference numeral 18a denotes the pin which is in electrical contact with the connecting conductor 17. A flat insulating plate 18 is provided between the connecting conductors 16 and 17 at one end and the laminations 14 at the other end. An elastically deformable synthetic resin block (19) is placed on top of the connecting conductors l6 and 17, which block is provided with closed cells. This means that block 19 includes a (large) number of compartments which are not in communication with the outside air. This block may consist of, for example, synthetic rubber and may have a volume of approximately 1.5 cubic/ems. The side of the synthetic resin block 19 remote from the connecting conductors 16 and 17 is denoted by the reference numeral 20. This part is provided with a layer which cannot substantially stretch. This layer consists of, for example, a polyester foil. FIG. 2 shows a ballast for stabilizing the are in a low-pressure mercury vapor discharge lamp during a given manufacturing stage. The coil as well as the tray-shaped housing 10 is completely finished in this case. The synthetic resin block 19 is already placed on the connecting conductors 16 and 17.

The next stage is to place the cover 1 (see FIG. I) on the tray-shaped part 10 of the housing (see FIG. 2) and this in such a manner that the holes 2 and 11, and 3 and 12, and 4 and 13 coincide with each other.

FIG. 3 shows the box-shaped ballast thus manufactured and now being provided with a cover. The reference numerals in FIG. 3 correspond to those of the previous Figures. In FIG. 3 the housing 10 is shown in a compartment 30. This compartment is connected at one end to a reservoir 31 which is filled with a liquid polyester mass and at the other end to a vaccum pump 32. The supply lead from the reservoir 31 to the compartment 30 includes a valve 33. The connection between compartment 30 and vacuum pump 32includes a valve 34. The compartment 30 has a clock-shaped wall 35 and a base 36. A plate 37 is provided between the housing 10 and the base 36 of compartment 30. The base 36 and the plate 37 can be moved up and down in a manner not further shown. As a result compartment 30 can be opened or closed. In the situation shownin FIG. 3 the compartment 30 is closed. The reference numerals 38 and 39 denote seals so as to shut off the compartment 30 in an airtight manner from the outside atmosphere. The supply pipe 40 protrudes through the hole 8 in the cover 1 of the ballast (see also FIG. 1 for this hole). Reference numeral 41 denotes a seal by which polyester mass is prevented from getting between the ballast and the wall of the compartment. The ballast is introduced into the compartment by firstly lowering the base 36, subsequently placing the ballast on the plate 37 and then raising the base 36 up to the position shown in FIG. 3. Reference numeral 19 again denotes the synthetic resin block.

When valve 42 is closed, valve 34 is opened and vacuum pump 32 is started. As a result the compartment 30 is substantially evacuated and hence, through chinks which are still present in the ballast, also the interior of this ballast. As a result the synthetic resin block 19 in the ballast will swell and envelops the connecting conductors, inter alia, 17. Subsequently valve 33 is opened. Due to the pressure below atmospheric pressure which prevails in the ballast the polyester mass is sucked in and flows to all parts of the ballast. As a result the pressure in the ballast will also increase to some extent. The polyester mass also moves about the synthetic resin block 19. When the entire ballast is filled with polyester mass, valve 33 and also valve 34 are closed and valve 42 which is in communication with the outside atmosphere is opened. As a result the interior of the compartment 30 reaches its normal atmospheric pressure again. Subsequently the base 36 is lowered and the tinished ballast is removed from the plate 37. The synthetic resin block 19 then surrounds the connecting conductors 16 and 17 with the polyester mass surrounding the resin block. After a period of waiting the polyester mass will have hardened and the ballast is ready for further transport and for use as a ballast for a discharge lamp. If desired, a plurality of ballasts instead of one ballast can be treated simultaneously in one compartment to be evacuated.

To illustrate the situation with reference to the synthetic resin block 19 more clearly, FIG. 4 shows the top-right part of the housing of FIG. 3 on a large scale. Also in this case the reference numerals are again the same as those in the previous Figures. FIG. 4 shows the situation prior to evacuation of the compartment 30 of FIG. 3 and FIG. 5 shows the same detail as in FIG. 4 but after the compartment 30 has been evacuated. It can be seen that in the case of FIG. 5 the synthetic resin block 19 has swollen and even extends to below the connecting conductor 17. It will be apparent from FIGS. 6 and 7 how the synthetic resin 19 moves about the connecting l6 and 17. These Figures are right-hand side elevational views of the housing 10 of FIG. 3, with the right-hand side wall being omitted. FIG. 6 shows a situation comparable to that of FIG. 4 namely the situation prior to evacuation of compartment 30. FIG. 7 shows a situation comparable to FIG. 5 namely after evacuation of compartment 30 (see FIG. 3). Prior to evacuation (see FIG. 6) the synthetic resin block had the original dimensions (see FIG. 2). After evacuation this block had swollen and envelops the conductors 16 and 17. Due to the non-stretchable layer a given curvature on the side of the block 19 facing the connecting conductors was obtained so that at the area of the insulating plate 18 (see FIG. 5) a satisfactory urging of these conductors is obtained while the synthetic resin block has entirely enveloped the connecting conductors between the plate 18 and the pin 18a.

FIG. 8 shows a further embodiment of the synthetic resin block. This block is denoted by reference numeral 50. The upper side also includes a substantially nonstretchable layer 51. The reference numerals 52 and 53 denote connecting conductors which are comparable to 16 and 17 of FIG. 2. The synthetic resin block 50 differs from block 19 by the presence of the two grooves 54 and 55 whose distance is substantially equal to that of the connecting conductors 52 and 53. The reference numeral 1 denotes a part of the cover for the housing of the ballast. When this block 50 was used instead of block 19 of FIG. 3, it would assume the shape upon evacuation as shown in FIG. 9. As a result of swelling and by the presence of the substantially nonstretchable layer 51 the grooves 54 and 55 open. Due to this swelling the grooves accommodate the conductors S2 and 53. if subsequently the polyester moulding mass flows into the housing, which is entirely in accordance with what has been described with reference to FIG. 3, the pressure on the block 50 will also again become approximately the same as the atmospheric pressure and the two grooves 54 and 55 will close so that the connecting conductors 52 and 53 are very satisfactorily enveloped.

The ballasts described will not damage the conductors, even in case of shrinkage cracks in the moulding mass.

What is claimed is:

1. An inductive ballast comprising a housing, a coil carried within said housing, electrical conductors for connection of electrical power to said coil extending from said coil, a block of elastically deformable synthetic resin having closed cells carried within said housing on said conductors in a space betwen said conductors and an adjacent wall of said housing so that when a vacuum is applied to said housing said space will be substantially filled by said block as a result of pressure developing within said cells and said elastically deformable block swelling and enveloping said conductors, and a molding mass of resinous material occupying the remaining spaces within said housing.

2. The ballast according to claim 1 wherein said block has a plurality of grooves in one side thereof extending in a direction parallel to said conductors so that upon the evacuation of said housing and swelling of said block said grooves will open so as to accommodate said conductors, said grooves being closed to encapsulate said conductors upon filling of said housing with said moulding mass, and further comprising means on said block on the side thereof remote from said conductors for preventing swelling of said side so that said side having said grooves will be curved upon expansion. a: 

1. An inductive ballast comprising a housing, a coil carried within said housing, electrical conductors for connection of electrical power to said coil extending from said coil, a block of elastically deformable synthetic resin having closed cells carried within said housing on said conductors in a space betwen said conductors and an adjacent wall of said housing so that when a vacuum is applied to said housing said space will be substantially filled by said block as a result of pressure developing within said cells and said elastically deformable block swelling and enveloping said conductors, and a molding mass of resinous material occupying the remaining spaces within said housing.
 2. The ballast according to claim 1 wherein said block has a plurality of grooves in one side thereof extending in a direction parallel to said conductors so that upon the evacuation of said housing and swelling of said block said grooves will open so as to accommodate said conductors, said grooves being closed to encapsulate said conductors upon filling of said housing with said moulding mass, and further comprising means on said block on the side thereof remote from said conductors for preventing swelling of said side so that said side having said grooves will be curved upon expansion. 